Are you looking for snowflakes for Snowmam?
Snow naturally occurs starting late November (almost the end of the month) - assuming you're playing in the right date, there should be snow in your town. Like rain, the weather will randomly cause it to visibly snow on certain days, and on those days you will see snow flurries falling, as well as snowflakes. To get a snowflake, you need to use your bug net to catch them.
If you're looking for snowballs to make snow people, two snowballs are randomly generated in town, you just have to run all over to find them, then you roll them in the snow until they are big enough to be pushed together. Depending on the sizes you made the snowballs, they will either be a snowman, snowmam, snowboy or snowtyke. You can learn more about them here:
http://www.thonky.com/animal-crossing-new-leaf/snow-people/
Hope that helped, wasn't really sure what you meant by 'how to get snow', so I just gave all the general info I know lol.